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Abstract

We analyzed the observations of scintillations in a laser beam (532 nm, ∼200mW power) traveling along a 144 km path at an altitude of 2.2–2.4 km above sea level, just above the atmospheric boundary layer, between the islands of La Palma and Tenerife. The observations were performed during nighttime on 18 July 2011, by means of a telescope with an aperture diameter of 1 m. Strong scintillations were observed. The estimates of spatial spectra and correlation functions indicated that the observed intensity fields possess, statistically, a locally isotropic structure, which agrees with the idea of a locally isotropic turbulence. The estimates of spatial autospectra and autocorrelation functions of the intensity field indicated that the characteristic scale of the internal structure of the observed clusters is 6.5–8 mm, while the characteristic size of the clusters is 4–5 cm. The major contribution to the observed scintillations comes from the inhomogeneities of the intensity field with scales from 1–2 cm up to 10–12 cm. The analysis of the cross-spectra indicated that the hypothesis of frozen turbulence introduced by Taylor can be used for the description of spatiotemporal structure of intensity fluctuations of laser beams traveling through long paths in the atmosphere.

Estimates of PSD [mm4/rad2] normalized for the dispersion of scintillations, observed during the study time interval. Light-gray isolines correspond to rectangle 1, gray ones to rectangle 2, black ones to rectangle 3. The radius of the circle shown by a bold black dash-dotted line equals 0.8rad/mm. Isoline marks correspond to the level numbers in the legend.

Estimates of 2D phase spectra φ(κ;δt). Left panel: δt=5ms (μ=1); right panel: δt=10ms (μ=2). The correspondence between shades of gray and rectangles is the same as in Fig. 4. Straight lines at κx=±0.3 in the left panel and at κx=±0.15 in the right-hand panel correspond to phase jumps of 2π.

Estimates of 1D phase spectra for δt=5ms evaluated for the three rectangles. The correspondence between shades of gray and rectangles is the same as in Fig. 4. The black dash-dotted line corresponds to φ¯(κx,δt)=u0κxδt, where u0 is the average drift velocity of the intensity clusters in the telescope aperture. The arrows mark the values of wave number κx=±0.3rad/mm, where the estimate of φ¯ has a jump of 2π.

2D PSD F(0)(κ;0) obtained from the observations during the study time interval. The correspondance between shades of gray and rectanges is the same as in Fig. 4. The radii of the circles shown by the black dash-dotted lines equal 0.8radmm−1 and 0.1radmm−1. Isoline marks correspond to the level numbers in the legend.